The present invention relates to a monitoring system for monitoring a field, particularly for the detection of motion of objects within a given area, the system comprising a detection stage provided with a camera for signal recording with respect to the area to be monitored, a processing stage provided with a storage device and a comparison circuit for producing comparison signals in dependence on signal differences and signal agreements, respectively, between signals produced by the camera and delayed and not delayed in the storage device and comprising a selective switchin-on stage having an intervention device actuacted in dependence on the number of comparison signals.
Such a motion detection system is disclosed in U.S. Pat. No. 2,493,543 and is mainly used in the field of protecting rooms from burglary or hold-ups.
Generally, the monitoring systems of a more simple nature are rather limited in range (for example devices operating with an infra-red beam) and can be easily avoided by persons to whom the presence and the mode of operation of the system is known. Consequently, the efficiency of such systems is often very poor.
To monitor a large-size area, use can be made of more elaborate systems using one or more cameras, but usually such systems require the presence of an operator for the interpretation of the result of the observation and the resultant proper decisions. In addition, it is possible to use automatic detection systems of the radar type which operate at a very high frequency. However, these systems are sensitive to parasitic signals and are therefore subject to untimely reactions.
On the other hand, none of the existing monitoring systems can distinguish between moving objects in the monitored area on the basis of their dimensions (the word "object" is used here in the most general sense: it may relate to a person, an animal or any object which performs a certain motion under the influence of a certain action). So these systems may not only start operating when a person moves into this area but also at a very untimely moment, for example when an animal passes by.